1. Field of the Invention
The present invention relates to a small magnetic disk cartridge that can be exchangeably loaded in a card disk drive that is inserted in the card slot of electronic equipment such as a digital still camera, a digital video camera, a laptop personal computer, etc.
2. Description of the Related Art
To record or reproduce information, a wide variety of recording media are removably loaded in the card slot of electronic equipment such as a digital still camera, a digital video camera, a laptop personal computer (PC), etc. Such recording media that are in practical use are a semiconductor memory type, a hard disk type, an optical disk type, a magnetic disk type (e.g., a floppy disk type), etc.
Among these recording media, the semiconductor memory type is most widely used, because it is easy to handle and has a relatively large recording capacity. However, the semiconductor memory type is relatively expensive. Therefore, in digital cameras employing the semiconductor memory type, the semiconductor memory is repeatedly used by storing the photographed image data in a PC, etc., and then deleting the data from the semiconductor memory.
Although some known hard disks can store 340 megabytes (MB) of data or 1 gigabytes (GB) of data, the hard disk type is similarly expensive. Likewise, the hard disk type is repeatedly used by storing data in a PC, etc., then deleting the data from the hard disk type memory.
The optical disk type has a large recording capacity for its size. For example, an optical disk with a size of 35 mmxc3x9741 mmxc3x9711 mm can store 256 MB of data. Optical disks with a recording capacity of 512 MB are about to be realized. However, optical disks have the disadvantage that the recording speed is slow, because the writing of data thereto is time-consuming.
Small magnetic disks (e.g., floppy disks) with a size of about 50 mmxc3x9755 mmxc3x972 mm can be exchangeably loaded in a disk drive of a size that can be inserted in the card slot of a PC, etc. However, the recording capacity is as small as 40 MB and insufficient to store data photographed by a camera. In addition, the size is not suitable for digital cameras.
With the spread of PCs, digital cameras have spread rapidly in recent years because of the easy method of recording, enhancement of the picture quality due to the development of imaging devices, enablement of data deletion and transmission, size of the recording capacity, etc. However, digital cameras are restricted in use, because recording media are restricted in cost and recording capacity, as described above. For instance, since recording media are very expensive, one camera is usually provided with one recording medium, which is repeatedly used. That is, when the recording medium is filled with data, the data is transferred to a PC and deleted from the recording medium. Because of this, there are cases where the recording medium is filled up during a trip. In addition, the recording medium cannot be stored as is, with data stored therein, nor can it be given away to a person.
Hence, there is a demand for the realization of a small recording medium which is large in recording capacity and low in cost so that the data photographed by a digital camera can be stored as is, or given away to a person. In PCs, there is also a demand for the realization of an inexpensive small large-capacity recording medium that can be handed to a person.
To meet the aforementioned demands, it is contemplated that the above-described small recording medium may comprise a card disk drive which is loaded in electronic equipment such as a PC and a digital camera, and a magnetic disk cartridge which is loaded in the card disk drive. That is, it is contemplated that such a magnetic disk cartridge may comprise a housing with a sliding shutter, and a flexible magnetic disk, rotatably supported within the housing, which is capable of high-density recording and has a recording capacity of 200 MB or larger. Examples of magnetic recording media with a high recording density are a magnetic recording medium with a thin metal film formed by vapor deposition or sputtering, and a magnetic recording medium employing barium ferrite powder or ferromagnetic magnetic powder. The magnetic recording medium with a high recording density employing barium ferrite powder is disclosed, for example, in U.S. patent application Ser. No. 10/266,584.
The xe2x80x9cmagnetic recording medium with a high recording density employing barium ferrite powderxe2x80x9d refers to a magnetic disk containing barium ferrite powder in a magnetic layer, and is formed from a material that is capable of a high recording density. The magnetic disk may be constructed of a magnetic recording medium. The disclosed magnetic recording medium has a non-magnetic substrate, a non-magnetic layer which contains both non-magnetic powder and a binder, and a magnetic layer which contains both ferromagnetic powder (which is hexagonal ferrite powder) and a binder. The non-magnetic layer and the magnetic layer are formed on at least one surface of the non-magnetic substrate in the recited order. In the non-magnetic layer, the quantity of carbon black whose average particle diameter is 10 to 30 nm is in a range of 10 to 50 weight parts with respect to 100 weight parts of the aforementioned non-magnetic powder. The thickness of the magnetic layer is 0.2 xcexcm or less. According to an electron-beam microanalysis, the standard deviation (b) of the strength of an element with respect to an average strength (a) which results from ferromagnetic powder is in a range of 0.03xe2x89xa6b/axe2x89xa60.4. The center plane average height Ra of the magnetic layer is 5 nm or less, and the 10-point average height Rz is 40 nm or less. In a magnetic disk employing the above-described magnetic recording medium, information is recorded or reproduced by employing a magnetic head, such as an MR head, a GMR head, and a TMR head, which is capable of a high recording density.
For instance, when the above-described magnetic recording medium is about 30 mm in diameter, it can have a high recording density of 200 MB or larger, preferably 500 MB or larger. Therefore, in the case of a still image having about 1 MB of data per image, the magnetic recording medium can store 500 images. In the case of a moving image, the magnetic recording medium can store image contents of about 30 minutes. Thus, the magnetic recording medium can store a moving image photographed by a digital camera, and a moving image which is transmitted by a portable telephone. As a result, users can conveniently use the magnetic recording medium. Furthermore, the magnetic recording medium can be conveniently used in PCs as an inexpensive large-capacity data storage medium. Thus, the convenience of the magnetic recording medium is great.
As previously described, card disk drives are loaded in electronic equipment such as a PC, a digital camera, etc. In the case of a PC shown in FIG. 1A, for instance, a card disk drive 6 is connected electrically with the socket 4 of the receiving portion of a card 2 that is inserted in the card slot of the PC. In the case of a digital camera 3 shown in FIG. 1B, a card disk drive 6 is connected electrically with the socket of the receiving portion 5 of the camera 3. In these card disk drives 6, a small magnetic disk cartridge 8 is removably loaded.
Therefore, the above-described card disk drive 6 is extremely small in size and has, for example, a length of 38 to 55 mm, a width of 35 to 51 mm, and a thickness of 3 to 5 mm. The above-described magnetic disk cartridge 8 has, for example, a length and a width of 25 to 36 mm and a thickness of 1 to 3 mm. This magnetic disk cartridge 8 is used to rotatably support a flexible magnetic disk (indicated by a hidden line in FIG. 1) within its housing.
In conventional magnetic disks with a high recording density, incidentally, the degradation of recording-reproduction characteristics due to fluctuations in the spacing between a magnetic disk and a magnetic head has become a problem. In addition, along with the narrowing of data tracks, slight circumferential fluctuations have also become problems as a cause of the degradation of recording-reproduction characteristics.
In addition, with a reduction in the width of a data track, the size of recorded signals is reduced. As a result, a dropout is caused by small dust particles which had been negligible in conventional magnetic disks.
Furthermore, with a reduction in size of magnetic disks, vertical alignment must be made with a high degree of accuracy when the magnetic disk cartridge 8 is loaded in the disk drive 6. That is, vertical alignment is usually made at two or three points, but since the distance between the points becomes short, both the disk drive 6 and the magnetic disk cartridge 8 require high accuracy.
A conventional small magnetic disk cartridge has, for instance, a structure such as that shown in FIG. 4. In this structure, a flexible magnetic disk 14 is rotatably supported within a flat housing 12. The housing 12 is constructed of an upper shell 12a and a lower shell 12b. The center portion of the magnetic disk 12 is mounted on a disk-mounting hub 15, which is spun by a spindle S provided in the above-described disk drive 6. The lower shell 12 is provided with a spindle hole 16 through which the disk-mounting hub 15 is magnetically chucked by the above-described spindle S. Note in all drawings that the thickness, etc., of each part are shown at ratios differing from actual dimensions to facilitate the understanding of the structure.
The disk-mounting hub 15 has a shaft portion 15a, which is chucked by the spindles of the disk drive 6. The hub 15 further has an annular portion 15b which is inserted into the center hole of the magnetic disk 14, and a flange portion 15c on which the radially inner circumferential portion of the magnetic disk 14 is mounted. Although not shown, liners and sliding sheets, etc., are interposed between the upper shell 12a and the upper side of the magnetic disk 14 and between the lower shell 12b and the under side of the magnetic disk 14. However, the conventional magnetic disk cartridge 8xe2x80x2 has the disadvantage that dust is liable to enter the housing 12 through the spindle hole 16. In the conventional magnetic disk cartridge 8xe2x80x2, the disk-mounting hub 15 is vertically movable with respect to the housing 12. When the magnetic disk cartridge 8xe2x80x2 is loaded in the disk drive 6, the housing 12 and disk-mounting hub 15 are vertically positioned separately from each other. Because of this, there is a possibility that the housing 12 and disk-mounting hub 15 will tilt individually. In such a case, there is a problem that stable rotation of the magnetic disk 14 cannot be obtained.
The present invention has been made in view of the above-described circumstances. Accordingly, it is the primary object of the present invention to provide a small magnetic disk cartridge which is thin in thickness and large in recording capacity, and which is capable of preventing dust from entering the housing and obtaining stable rotation.
To achieve this end and in accordance with the present invention, there is provided a small magnetic disk cartridge for use in a card disk drive to be loaded in electronic equipment. The magnetic disk cartridge includes a housing, a disk-mounting hub which is rotated by a spindle provided in the disk drive, and a flexible magnetic disk mounted on the disk-mounting hub. The disk-mounting hub is rotatably supported by the housing through a bearing equipped with inner and outer races which are mutually rotatable.
The outer race may be fixed to the housing, while the inner race may be fixed to the disk-mounting hub. Conversely, the inner race may be fixed to the housing, and the outer race may be fixed to the disk-mounting hub.
According to the magnetic disk cartridge of the present invention, the disk-mounting hub is rotatably supported by the housing through the ball bearing equipped with inner and outer races which are mutually rotatable. Therefore, the center hole of the housing is closed with the disk-mounting hub and the bearing. As a result, the entry of dust into the housing can be prevented.
The disk-mounting hub is integrated with the bearing fixed to the housing. Therefore, when the magnetic disk is loaded in the disk drive, the magnetic disk can be vertically positioned with a high degree of accuracy. In the case where the housing tilts, the magnetic disk also tilts simultaneously and therefore the interior space of the housing does not change. As a result, stable rotation of the magnetic disk is obtained and makes it possible to assure a stable head touch.
Since the bearing and the disk-mounting hub are integrated with each other, the magnetic disk can be prevented from touching the liners or sliding sheets during conveyance.